Abstract
Quorum quenching (QQ) is a promising strategy for preventing and controlling quorum sensing (QS)-mediated bacterial infections. It interferes with QS by the inhibition of signal synthesis, the detection of enzyme-catalyzed degradation, and the modification of signals. N-Acyl homoserine lactones (AHLs) represent a family of widely conserved QS signals involved in the regulation of virulence factor production in many Gram-negative bacterial pathogens. In this study, AHL-degrading bacterial strains were isolated, and the most efficient one was evaluated for its potential against QS-mediated pathogens. Results showed that an AHL-degrading bacteria Ochrobactrum intermedium D-2 effectively attenuated maceration produced by the pathogen Pectobacterium carotovorum subsp. carotovorum (Pcc) on radish and potato slices. Strain D-2 exhibited a superior AHL degradation activity and efficiently degraded various AHLs, including N-hexanoyl-L-homoserine lactone (C6HSL), N-(3-oxohexanoyl)-L-homoserine lactone (3OC6HSL), N-(3-oxooctanoyl)-L-homoserine lactone (3OC8HSL), and N-(3-oxododecanoyl)-L-homoserine lactone (3OC12HSL). Analysis of the degradation products of AHL by gas chromatography-mass spectrometry led to the identification of N-cyclohexyl-propanamide and propanamide as the main intermediate products, suggesting that AHL was degraded by hydrolysis. Annotation and analysis of the whole genome sequence of strain D-2 revealed the presence of an AHL-lactonase, termed AidF. Moreover, the application of strain D-2 was able to substantially reduce the disease severity caused by Pcc on host plants. These results reveal the biochemical basis of a highly efficient AHL-degrading bacterial isolate and present the potential to attenuate Pcc virulence through QQ.
Highlights
The gram-negative strain Pectobacterium carotovorum subsp. carotovorum (Pcc) is a broad host range pathogen that causes soft rot, wilt, and blackleg in various cruciferous vegetables such as Chinese cabbage, potato, carrot, tomato onion, rhubarb, and cucumber (Lim et al, 2013)
Quorum quenching (QQ) can be achieved by inhibiting the synthesis or detection of signal molecules and by the enzyme-catalyzed degradation or modification of signal molecules (LaSarre and Federle, 2013; Grandclement et al, 2016)
Areas of macerated tissue (Figure 4B) were 17.9% and 17.5% in the treatment with Z3-3, and the mixture of E. coli DH5α and Z3-3, respectively. These results indicated that QQ strain D2 is a potent biological control agent against pathogen Pcc and may have the potential to be used to control Acyl homoserine lactones (AHLs)-dependent bacterial pathogens
Summary
The gram-negative strain Pectobacterium carotovorum subsp. carotovorum (Pcc) (formerly known as Erwinia carotovora subsp. carotovora) is a broad host range pathogen that causes soft rot, wilt, and blackleg in various cruciferous vegetables such as Chinese cabbage, potato, carrot, tomato onion, rhubarb, and cucumber (Lim et al, 2013). Pcc has been reported to cause wet rot disease in banana plants (Basim et al, 2019). In 2016, severe wet rot (tip over) in banana plants caused by Pcc was recorded in greenhouses in Turkey (Basim et al, 2019). A wide range of microbes uses the QS system as a defense or attack mechanism for antibiotics production, bioluminescence expression, biofilm formation, or the expression of virulence and pathogenicity factors (Deng et al, 2011; Liu et al, 2015; An et al, 2020). The attack mechanism and expression of virulence and pathogenicity initiate after sensing and binding the signal molecules to receptors (Jayaraman and Wood, 2008; Deng et al, 2011). The interruption of the “attack mechanism” in QS-mediated pathogens is a feasible strategy to protect hosts against infectious diseases
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